Vaporizer tube system



Aug. 1l, 1953 F. H. KEAsT rs1-AL VAPORIZER TUBE SYSTEM Filed Jan. 6. 1951 Tron/gez Patented ug. 11, 1953 vAroRIzER TUBE SYSTEM Francis Henry Keast, Toronto, Ontario, and Frederick Denison Morgan Williams, Weston, Ontario, Canada, assignors to A. V. Roe Canada Limited, Malton, Ontario, Canada, a corporation Application January 6, 1951, Serial No. 204,732

11 Claims. (Cl. 60,39.71

This invention relates to fuel vapourizing systems for combustion chambers and particularly to combustion chambers of gas turbine engines.

In order to introduce fuel into the llame tube of a combustion chamber in the form of a vapour which can be readily ignited, a Well established practice of the art is to provide vapourizer tubes mounted at their forward or upstream ends in a tube plate and extending downstream into the llame zone. These tubes extend from the front face of the tube plate; the remainder of the tube plate forms a closure across the upstream end of the flame tube so that air flowing into the upstream end or inlet of the name tube is directed into the vapourizer tubes and flows through them into the llame zone. The downstream ends of the vapourizer tubes are curved through 180 or, as shown in co-pending application Serial Number 139,843, dated January 21, 1950, now Patent No. 2,548,087, by F. D. M. Williams, they con- K verge upon a common outlet nozzle, to discharge the air upstream into the flame zone. Liquid fuel is introduced to the upstream ends of the vapourizer tubes through suitable jets and is A, carried down the tubes by the ow of air. Since the greater part of the outer surfaces of the vapourizer tubes is exposed to the combustion in the flame zone the tubes become very hot and the liquid fuel flowing through them is vapourized so that a mixture of air and fuel vapour is discharged as a combustible gas. In the process of vapourization of the fuel the tubes are cooled against overheating.

It has been established by measurement that gas temperatures are very high near the centre of vapourizer tubes, and that in the outer regions of the flame zone, beyond a certain radius, they are progressively lower. In the prior yart constructions the 180 bends or the portions of the tubes converging upon the common nozzle are situated in the hottest part of the ame zone, yet by centrifugal action the liquid fuel tends tov be thrown to the outside of the bends, that is to the downstream walls, resulting in uneven and infuel of the portions of the tubes exposed to the most severe external conditions. From this cause, frequent tube failures have occurred due to burning of the tubes on the upstream sides of the bends.

The object of this invention is to insure adequate scrubbing of the upstream walls of the vapourizer tubes situated in the hottest part of the flame zone. Other objects and advantagessof lsu of the ame zone and on the axis of the group .45 adequate internal scrubbing by unvapourized the invention will be apparent from the following description of a preferred example.

In the following drawing forming a partof this specification and in which like reference vcharacters designate like parts throughout the same:

Figure 1 is a side elevation, partly broken away, of a typical gas turbine engine embodying a vapourizer tube system according to the invention;

Figure 2 is a longitudinal section through a typical gas turbine engine combustion chamber embodying the invention, and showing kthe vapourizer tube system partly in elevation and partly in section; and

Figure 3 is an enlarged perspective View ofthe vapourizer tube assembly shown in Fig. 1, including a cut-away portion of the baille.

.Referring to the drawing, air from the .compressor of the engine enters the combustion chamber I0 in the direction of the arrow Il. The combustion chamber I8 is insulated by the annular space l2 from the llame tube I3, the upstream end I4 of which is open to admit a portion of the air entering the chamber. A transverse baille I5, having four radially disposed, substantially triangular openings or slots 15a, supports the tube plate I6 to which the vapourizer tube assembly I1 is coaxially secured. The four individual vapourizer tubes I8 are disposed on the same radii as the slots 15a and extend through the tube plate 16protruding a slight distance in an upstream directiontherethrough, and their open inlet ends I9 face the air stream nowing from the compressor through the combustion chamber.

Liquid fuel may be introduced to the vapourizer tube system through the pipeline 20 leading into the burner 2| the burner shown in the drawing is of the torch igniter type requiring an ignition lead which is carried in the tube 22 from the external terminal 23. Jets 24 are provided in the burner 2| to inject fuel into the upstream ends I9 of the vapourizer tubes and since the jets are slightly offset from the axes of their respective vapourizer tubes they present relatively little obstruction to the free entry of the air.

Downstreamy of the tube plate I5 the'vapourizer tubes are arranged to diverge arcuatelyfrom the axis of their annular mounting in the tube plate, each tube extending in an oblique direction, along a downstream projection of its corresponding slot |5a in the bailie 15; after traversing the slot the tube enters another arcuate bend toassume a position adjacent and substantially parallel to the wall Aof the llame tube 13' t0 provide a longitudinally directed portion |8a; the portion |8a of each tube terminates in an arcuate bend |8b through approximately 180 around an axis of curvature which represents a radius of the flame tube, whereby each tube turns in a substantially circumferential direction, in the same sense as the other tubes, and is continued through the bend |8b in an upstream direction to provide a longitudinally directed intermediate portion |80, also adjacent and parallel to the wall of the flame tube. Thus the longitudinally directed portions |801, and |80 are annularly disposed in the outer region of the flame zone where the combustion temperatures are relatively low. The portion |8c of each tube extending in an upstream direction terminates in an arcuate bend Id, from which bends the tubes converge obliquely upon a common nozzle 25 to provide outlet terminal portions |88 lying cross-stream in a plane substantially transverse to the axis of the combustion chamber. The nozzle 25 consists of a substantially tubular hollow body, which may be substantially cylindrical or slightly frusto-conical in form, closed at its downstream end and open at its upstream end which faces in an upstream sense; the outlet terminal portions |8e of the vapourizer tubes enter the nozzle substantially tangentially to induce swirl and thereby to promote thorough mixing and to ensure that any residual unvapourized fuel which may enter the nozzle will scrub its internal cylindrical surfaces and be vapourized before the fuel-air mixture emerges as a vortex into the flame zone. The dimensions of the nozzle and of the variously directed portions of the vapourizer tubes are so chosen that the outlet terminal portions |8e of the tubes are of significant length, at least three times the diameter of the vapourizer tubes.

In operation, the greater portion of the air entering the combustion chamber flows into the an nular space |2 between the combustion chamber I and the flame tube i3 and thence, through the various stages of the orifices 2S, into the name tube opposite or downstream of the vaporizer tube assembly H; the remainder enters the upstream end I4 of the flame tube I3 and, while a part of this air flows through the slots 5a, a part enters the vaporizer tubes i8 through the open inlet ends I9. Liquid fuel is injected by the .jets 24 into the same inlet ends, so that a mixture of fuel and air flows through the vapourizer system. finally emerging from the outlet nozzle 25. Combustion is initiated by means of the torch igniter, and thereafter continues in a self-propagating manner in accordance with normal gas turbine practice.

Since the tubes I8 are exposed to the flame zone they become very hot and the liquid fuel flowing through them is vapourized in the course of its passage from the inlet ends I9 to the outlet nozzle 25. However, because the tubes diverge from their mounting in the tube plate l and tend through a relatively cool region of the flame zone, adjacent the flame tube wall, a fairly large proportion of the liquid fuel arrives at the bends |8b in liquid form; the liquid fuel is carried to the outside of the bends under centrifugal action, but these bends are not situated in a high telL perature region and the ineffective vapourization cooling of their upstream walls resulting from the uneven distribution of the liquid fuel is not important. After passing the bends |550, the mixture of air and fuel vapor and liquid fuel is projected in an upstream direction through the intermediate portions before entering the outlet terminal portions |86 of the vapourizer tubes, which lie in the region of highest temperature. The liquid fuel is completely Vapourized in the terminal portions ISe and the mixture enters the nozzle 25, whence it is discharged into the flame ZOIle.

The radially disposed slots |511, being on the same radii as the diverging portions of the Vapourizer tubes i8, serve the double purpose of admitting primary air to the iiame zone (the effect of the baffle l5 being to form a region of low pressure in the air stream, in which stable combustion can take place) and to direct a flow of air upon the diverging portions of the vapourizer tubes, to effect some cooling of the tubes in this region and to prevent the formation of carbon deposits thereupon.

It will be understood that the upstream outer surfaces of the outlet terminal portions |8e of the vapourizer tubes are exposed to the region of most intense flame in the flame zone. By this construction the direction of flow of the mixture of air and fuel entering these portions of the vapourizer tubes is so altered by the arcuate bends |8cl that any liquid fuel is projected by centrifugal action against the upstream inner surfaces to provide a thorough scrubbing action on the most severely heated Walls. The radii of the bends IM may vary considerably in Order to produce the desired result but they are normally made as small as possible, approaching the mini mum bend radii of the tube sections concerned. The portions |86 are made as long as conveniently possible in order to produce a large heat transfer in this high temperature region of the flame zone, thereby promoting vapourization of the liquid fuel. It has been found that the length of the outlet terminal portion of each tube should be at least three times the diameter of the tube to give the most satisfactory results. The essence of the invention lies in the conformation of the tubes or similar vapourizing ducts by which the fuel-air l ixture contained therein is directed against the upstream sides of the main vapourizing portions of the tubes thereby subjecting the vapourizing,t surfaces to an effective scrubbing action by the liquid fuel during vapourization; and in the situation of the main vapourizing portion in the hottest regions of the flame zone, while the remainder of the vapourizing system is so situated that it .is not exposed to unduly high temperatures. By this means burning and corrosion of the vapourizer tubes may be avoided and more complete vapourization of the liquid fuel achieved.

It will be undersood that the form of the invention herewith shown and described is to be taken as a preferred example of the same, applied to a tube type combustion chamber and that it may be similarly applied to an annular combus tion chamber; furthermore the convergence of the tubes to a common nozzle is not an essential feature of the invention and various other changes in the shape, size and arrangement of the parts may be resorted to without departing from the spirit of the invention or the scope of the claims.

What we claim as our invention is:

1. A vapourizer system for a combustion chamber into which liquid fuel is introduced and burned as a vapour in an air stream flowing in the combustion chamber comprising, a plurality of vapourizer tubes each having an inlet at one end and being secured within the combustion chamber with the inlet facing the air stream, and

assale? a nozzle having an outlet facing upstream, the tubes having terminal portions converging substantially transversely of the air stream into' the nozzle and having intermediate portions adj-'aim ing the terminal portions, the Senses toward the terminal portions of the longitudinal axes ofthe intermediate portions cach having a component directed upstream.

2. A vapourizer system for a combustion cham'- ber into which liquid fuel is introduced and burned as a vapour in an air stream flowing in the combustion chamber comprising, a plurality of vapourizer tubes having open inlet ends and secured within the combustion chamber with the inlet ends facing the air stream, and a tubular nozzle within the combustion chamber and hav ing an outlet facing upstream, the tubes'havirig terminal portions converging noner'a'di'ally and substantially transversely of the air streamint'o the circumferential walls of the nozzle and having intermediate portions adjoining the terminal portions and extending in an upstream sense t'oward the terminal portions.

3. A Vapourizer system for a combustion chamber in which fuel is burned in a stream of air flowing longitudinally through the combustion chamber, comprising a baille disposed within the combustion chamber substantially transversely thereof and having annularly spaced openings for the admission of a part of the air stream, vapourizer tubes having open inlet ends mounted in the baffle and having a common outlet facing upstream, each tube having a terminal portir-'i joining the outlet and an intermediate portion adjoining the terminal portion and extending in an upstream sense toward the terminal portion, the inlet ends of the tubes being annularly spaced in the baffle and facing the air stream, each inlet end being radially spaced towards the longitudinal axis of the combustion chamber from an associated one of the openings in the baille, the tubes diverging radially downstream of the baffle and each extending across one of said openings to provide portions directly downstream of the associated openings in the baille and then extending downstream to provide longitudinally directed portions of the tubes, the tubes then extending from the longitudinally directed portions successively to the intermediate portions and *n the terminal portions.

Ll. A vapourizer system for a combustion chamber in which fuel is burned in an air stream flowing longitudinally through the combustion chamber and in which the combustion chamber has a flame zone in which the fuel is burned as a vap-our, the flame zone having a central region of maximum temperature and outer regions surrounding the central region, the vapourizer system comprising vapourizer tubes having open inlet ends and secured within the combustion chamber with the inlet ends facing the air stream, and a nozzle within the combustion chamber and having an outlet facing upstream, the nozzle being in longitudinal alignment with the flame zone, the tubes having terminal portions disposed across a portion of the central region of the flame zone and extending into the nozzle and having intermediate portions adjoining the terminal portions and extending in an upstream sense toward the terminal portions, the major portions of the vapourizer tubes not including the terminal portions lbeing annularly spaced in the outer regions of the flame zone.

5. A vapourizer system for a combustion chamber into which liquid f-uel is introduced and burned as a vapour in an air stream owing in the combustion chamber comprising, a plurality of vapourizer tubes having open inlet endsL and secured within the combustion chamberwith the inlet ends facing the air stream so as to admit a portion of the air stream, means for introduc ing liquid fuel to the inlet ends, and a nozzle Within the combustion chamber and having an outlet facing upstream, the tubes having terminal portions converging substantially transversely of the air stream into the nozzle andhaving intermediate portions adjoining the terminal portions and extending in an upstream sense toward the terminal portions so that the fuel andan' flowing therein are directed by centrifugal force upon the upstream sides of the terminal portions of 'the tubes before being introduced into the nozzle, the length of each of the terminal portionsof the tubes being at least three times the diameter of the tubes;

6. A combustion chamber as claimed in claim 5 wherein the nozzle is tubular and the terminal portions of the vapourizer tubes converge inonradially upon the side walls of the nozzle to introduce the fuel therein thereby inducing a swirling action of the fuel within the nozzle.

'7. A vapourizer system for a combustion chamber in which fuel is burned in an air stream flowing longitudinally through the combustion chamber and which has a flame zone extending longitudinally through the said chamber i-n which the fuel is burned :as a vapour, the vapourizer system comprising a vapourizer tube having an open inlet end facing the air stream, an intermediate portion, a vapourizing terminal portion of a length substantially exceeding its diameter, an outlet facing upstream and located near the longitudinal axis of the llame tube and producing in the llame zone downstream of the outlet a radially central region of maxi-- mum temperature annularly surrounded by a radially outer cooler region, and means for introducing liquid fuel into the inlet end, substan tially all the vapourizer tube not including the terminal portion being at a materially greaterl radial distance from the said axis than the out-- let so as to be disposed in the said outer region.

of the flame zone, the terminal portion extending from the intermediate portion to the outlety whereby the terminal portion extends for a. sub

stantial distance transversely across a portion of,

the central region of the flame zone to provide vapourization of the liquid fuel by the heat of the said central region, the intermediate portion extending in an upstream sense toward the terminal portion so that the fuel and air flowing therein are directed by centrifugal force upon the upstream side of the terminal portion before reaching the outlet.

8. A vapourizer system as claimed in claim '7 in which the length of the terminal portion of the tube is at least three times the diameter of the tube.

9. A vapourizer system for a combustion chamber in which fuel is burned in an air stream flowing longitudinally through the combustion chamber and in which the combustion chamber has a flame zone in which the fuel is burned as a vapour, the llame zone having a central region of maximum temperature and an outer region surrounding the central region, the vapourizing system comprising a baille disposed within the combustion chamber substantially transversely thereof and having annular spaced openings for the admission of a part of the air stream, vapourzer tubes each having an open nlet*l `nd mounted in the baille and each having an intermediate portion, a terminal portion, and an outlet disposed in the said central region of the llame zone and facing upstream, and means for introducing liquid fuel into the inlet ends, the inlet ends of the tubes being annularly spaced in the baffle and facing the air stream, each inlet end being radially spaced towards the longitudiintroducing liquid fuel into the inlet ends, the nal axis of the combustion chamber from an associated one of the openings in the baille, the tubes diverging radially downstream of the baille and each extending across one of the said openings to dispose portions directly downstream of the associated openings in the baffle and then extending downstream to provide longitudinally directed portions of the tubes, the tubes then extending from the longitudinally directed portions successively to the intermediate portions and to the terminal portions, the intermediate portions extending in an upstream sense toward the terminal portions so that the fuel and air flowing therein are directed by centrifugal force upon the upstream sides of the terminal portions before reaching the outlets.

10. A vapourizer system for a combustion chamber in which fuel is burned in an air stream flowing longitudinally through the combustion chamber and which has a llame zone extending longitudinally through the said chamber' in which the fuel is burned as a vapour, the vapourizing system comprising a vapourizer tube having an open inlet end facing the air stream and extending to an outlet disposed relatively near the central longitudinal axis of thev flame zone, thus producing in the flame Zone a radially central region of maximum temperature extending longitudinally downstream from the location of the outlet end and annularly surrounded by a radially outer cooler region, and means for introducing liquid fuel into the inlet end, the Vapourizer tube extending downstream from the inlet end and including a bend of approximately 180 located at a materially greater distance from the said axis than the outlet so as to be wholly disposed in the said outer region of the flame zone, an intermediate portion, and a terminal portion of a length substantially exceeding its diameter, the intermediate portion extending upstream from the bend also within the said outer region of the flame zone and leading into the terminal portion, the latter extending from the intermediate portion to the outlet transversely across a portion of the central region of the flame zone to provide vapourization of the liquid fuel by the heat of the said central region.

1l. A vapourizing system as claimed in claim l0 in which a length of the terminal portion of the tube is at least three times the diameter of the tube.

FRANCIS HENRY KEAST. FREDERICK DENISON MORGAN WILLIAMS.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,404,335 Whittle July 16, 1946 2,503,006 Stalker Apr. 4 1950 2,522,081 Allen Sept. 12, 1950 2,541,900 Williams Feb. 13, 1951 2,548,087 Williams Apr. 10, 1951 2,593,849 Clarke Apr. 22, 1952 2,595,765 Clark May 6, 1952 

